GETTING TO KNOW YOU: INTRODUCING A SILVERBACK TO AN ESTABLISHED GROUP OF ADULT FEMALE GORILLAS

An attempt in 2015 to introduce a new silverback to an established group of six western lowland gorillas (Gorilla gorilla gorilla) housed at the Gladys Porter Zoo, 3 months following his move to the gorilla building, was judged a failure, and a decision was made to retreat to earlier stages of the introduction process, allowing only protected contact between the male and the group. On May 1, 2018 another introduction was initiated, this time to a smaller group of three adult females. Twelve months of behavioral data collected by means of focal animal sampling, totaling 148 hours (N=4, indoors and outdoors), grouped into eight behavior categories, were divided into three 4-month periods: Period 1=before full contact, Period 2=immediately following full contact, and Period 3=continued full contact. Descriptive summary statistics (percent total observation time, summed across subjects) compared across periods reveal an increase in affiliative behavior indoors: Period 1 = 68.6%, and Period 3 = 119.3%, and a decrease in tense/anxious behavior outdoors: Period 1 = 50.8%, Period 3 = 13.5%. Surprisingly, in contrast to other reports, levels of agonistic behavior were low in all conditions, indoor Periods 1-3 = 1.7% to 1.6%; outdoor Periods 1-3 = 1.2% to 0.3%. Although not without skirmishes, this introduction is judged successful. The prolonged period of protected contact and a reduced group size may have facilitated group formation.